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Biomedical subjects

R J Tusa

Publications and source records attributed to R J Tusa.

At least 19 recordsLinked to original sources
PubMed2001

Perverted head-shaking nystagmus: a possible mechanism.

The authors describe a patient with acute MS who developed vertigo (tumbling) and downbeat nystagmus upon horizontal head oscillation (perverted head-shaking nystagmus). The only abnormality on brain MRI was a hyperintense signal in the caudal medulla that contains the nucleus Roller and nucleus intercalatus. These nuclei project to structures involved in the velocity storage system for horizontal vestibulocular reflex (VOR) and vertical VOR, and also to the vestibular cerebellum. The authors offer possible mechanisms for perverted nystagmus in this patient.

Adult↗
PubMed2001

Role of central preprogramming in dynamic visual acuity with vestibular loss.

OBJECTIVE: To determine the contribution of central preprogramming of eye movements to dynamic visual acuity (DVA) during head movement in patients with vestibular hypofunction. STUDY DESIGN: Prospective, clinical study. SETTING: Tertiary care, academic hospitals. PARTICIPANTS: Twenty-six healthy subjects and 20 patients with unilateral (UVL) and 7 with bilateral vestibular loss (BVL) (age range, 20-86 years). INTERVENTIONS: Diagnostic interventions, including caloric and rotational chair testing. MAIN OUTCOME MEASURE: Measurements of DVA during predictable (DVA-predictable) and unpredictable (DVA-unpredictable) head movements using a computerized test. RESULTS: There was a difference between DVA-predictable and DVA-unpredictable scores in all groups (P<.02). The difference between DVA-predictable and DVA-unpredictable scores for the BVL group was significantly greater than that for the other groups (P<.005). Age was a significant factor in DVA-unpredictable scores for the healthy subjects (P<.001) and UVL group (P<.02). Comparisons of DVA between groups were significant (P<.03), with the following exceptions: UVL group for head movements toward the unaffected side for DVA-predictable and DVA-unpredictable scores, compared with healthy subjects, and UVL group for head movements toward the affected side for DVA-predictable scores, compared with the BVL group. CONCLUSIONS: Unpredictable head movements cause a greater decrement in visual acuity than do predictable head movements. This suggests that central programming of eye movements and/or efference copy contributes to gaze stability during predictable head movements in healthy subjects and patients with vestibular hypofunction. Patients with BVL use central programming of eye movements to maintain gaze stability more than do healthy subjects or patients with UVL.

Adult↗
PubMed2001

Benign paroxysmal positional vertigo.

Benign paroxysmal positional vertigo (BPPV) is the most common and most treatable cause of vertigo. In most cases, a simple maneuver that takes less than a few minutes to do resolves the problem. BPPV is caused by misplaced calcium carbonate crystals (otoconia) in the semicircular canal of the inner ear that have broken free from the utricle. When these crystals break free, they either remain loose in one of three different semicircular canals or attach to the hair cells within a canal. Several different types of treatment maneuvers have been described. The maneuver to use varies according to the semicircular canal involved and whether the crystals are loose or attached to the hair cells.

Humans↗
PubMed2001

Vertigo.

Vertigo is a common symptom among outpatients. There are several causes for vertigo, and each cause requires a specific treatment. Depending on the cause, treatment includes change in drugs, physical therapy, bedside maneuvers, life style, and diet. All forms of treatment can be done by neurologists in an outpatient setting.

Acute Disease↗
PubMed2001

Gaze-stabilizing deficits and latent nystagmus in monkeys with brief, early-onset visual deprivation: eye movement recordings.

The normal development and the capacity to calibrate gaze-stabilizing systems may depend on normal vision during infancy. At the end of 1 yr of dark rearing, cats have gaze-stabilizing deficits similar to that of the newborn human infant including decreased monocular optokinetic nystagmus (OKN) in the nasal to temporal (N-T) direction and decreased velocity storage in the vestibuloocular reflex (VOR). The purpose of this study is to determine to what extent restricted vision during the first 2 mo of life in monkeys affects the development of gaze-stabilizing systems. The eyelids of both eyes were sutured closed in three rhesus monkeys (Macaca mulatta) at birth. Eyelids were opened at 25 days in one monkey and 40 and 55 days in the other two animals. Eye movements were recorded from each eye using scleral search coils. The VOR, OKN, and fixation were examined at 6 and 12 mo of age. We also examined ocular alignment, refraction, and visual acuity in these animals. At 1 yr of age, visual acuity ranged from 0.3 to 0.6 LogMAR (20/40-20/80). All animals showed a defect in monocular OKN in the N-T direction. The velocity-storage component of OKN (i.e., OKAN) was the most impaired. All animals had a mild reduction in VOR gain but had a normal time constant. The animals deprived for 40 and 55 days had a persistent strabismus. All animals showed a nystagmus similar to latent nystagmus (LN) in human subjects. The amount of LN and OKN defect correlated positively with the duration of deprivation. In addition, the animal deprived for 55 days demonstrated a pattern of nystagmus similar to congenital nystagmus in human subjects. We found that restricted visual input during the first 2 mo of life impairs certain gaze-stabilizing systems and causes LN in primates.

Animals↗
PubMed2001

Gaze-stabilizing deficits and latent nystagmus in monkeys with early-onset visual deprivation: role of the pretectal not.

We studied the role of the pretectal nucleus of the optic tract (NOT) in the development of monocular optokinetic nystagmus (OKN) asymmetries and latent nystagmus (LN) in two monkeys reared with binocular deprivation (BD) caused by binocular eyelid suture for either the first 25 or 55 days of life. Single-unit recordings were performed in the right and left NOT of both monkeys at 2-3 yr of age and compared with similar unit recordings in normally reared monkeys. We also examined ocular motor behavior during electrical stimulation of the NOT and during pharmacological inactivation and activation using GABA(A) agonists and antagonists. In BD animals a large proportion of NOT units was dominated by the contralateral eye, in striking contrast to normal animals where 100% of NOT units were sensitive to stimuli delivered to either eye. In the 55-day BD animal no binocularly sensitive neurons were found, while in the 25-day BD animal 60% of NOT units retained at least some binocular sensitivity. Differences in direction sensitivity were also observed in BD animals. We found that 56% of units in the 55-day BD monkey and 10% of units in the 25-day BD monkey responded preferentially to contraversive visual motion. In contrast, only 5% of the NOT units encountered in normally reared monkeys respond preferentially during contraversive visual motion, the rest were most sensitive to ipsiversive visual motion. NOT neurons of BD monkeys showed a wide range of speed sensitivities similar to that of normal monkeys. Unilateral electrical stimulation of the NOT in BD animals induced a conjugate nystagmus with slow phases directed toward the side of stimulation. When we blocked the activity of NOT units with muscimol, a potent GABA(A) agonist, LN was abolished. In contrast, LN was increased when spontaneous activity of the NOT was enhanced with bicuculline, a GABA(A) antagonist. Our results indicate that the NOT in BD monkeys plays an important role in the OKN deficits and LN generation during monocular viewing. We hypothesize that the large proportion of units dominated by the contralateral eye contribute to the development of monocular OKN asymmetries and LN.

Animals↗
PubMed2001

Strategies for balance rehabilitation: fall risk and treatment.

Identification of fall risk for patients with known vestibular hypofunction is important because it affects the management and the level of independence of these patients. Patients with bilateral vestibular loss, overall, have a greater incidence of falls than the general community-dwelling population over the age of 65 years. In younger patients, the incidence of falls may be related to severity of vestibular loss and to overconfidence or a lack of caution in activities. Preliminary reports suggest that vestibular rehabilitation can reduce the fall risk in patients with vestibular loss.

Accidental Falls↗
PubMed2000

The effect of the canalith repositioning maneuver on resolving postural instability in patients with benign paroxysmal positional vertigo.

OBJECTIVE: Patients with benign paroxysmal positional vertigo (BPPV) often experience postural instability as well as brief episodes of vertigo. The purpose of this study was to determine whether successful resolution of the episodic vertigo, through use of the canalith repositioning treatment, would be accompanied by improvement in postural stability. STUDY DESIGN: Prospective clinical study. SETTING: Outpatient tertiary care facility in a university. PATIENTS: Thirty-three patients with a diagnosis of the canalithiasis form of BPPV affecting the posterior canal unilaterally. All patients had complete remission of the positional vertigo after treatment. Patients with abnormal caloric or rotary chair test results were excluded from the study. INTERVENTION: The posterior canal BPPV was treated by the canalith repositioning treatment. MAIN OUTCOME MEASURES: Postural stability was assessed by computerized dynamic posturography before and 1 to 2 weeks after treatment. Six different subtests were used. RESULTS: A significant number of patients had abnormal stability, as measured with computerized dynamic posturography, before treatment. After treatment there was a significant increase in the number of subjects with normal results on the different subtests; however, not all patients had normal postural stability. Younger subjects were more likely to show improved stability. CONCLUSIONS: Treatment of BPPV using the canalith repositioning treatment results in improved postural stability in patients with BPPV. Not all patients have normal stability after treatment, however, and assessment and treatment of the balance problems may be necessary.

Adult↗
PubMed2000

Falls in patients with vestibular deficits.

OBJECTIVE: To determine to what extent patients with vestibular hypofunction experience falls. STUDY DESIGN: Prospective clinical study. SETTING: Outpatient tertiary care facility in a university. PATIENTS: Patients with unilateral (n = 70) and bilateral (n = 45) vestibular hypofunction, confirmed on vestibular function testing, aged 24 to 89 years. INTERVENTION: None. MAIN OUTCOME MEASURE: Incidence of falls. RESULTS: There was a significant difference in the incidence of falls reported since the onset of the vestibular deficit by patients with unilateral (UVL) and bilateral (BVL) vestibular hypofunction. The incidence of falls for BVL was significantly greater than that for UVL. The incidence of falls for UVL was not different from that expected in a community-based population when age was considered. The incidence of falls for BVL was significantly greater than that reported for the general population aged 65 through 74 years (51.1% for BVL, 25% for community-dwelling individuals) but was significantly less than expected for persons aged > or =75 years (18.2% for BVL, 49% for community-dwelling individuals). The lower incidence of falls in patients with BVL aged > or =75 years may be related to the use of assistive devices and to a decrease in risky behavior. All patients with serious injury were from the UVL group, and all were >65 years old. The incidence of fall-related injuries requiring medical attention among patients with UVL was similar to that in community-dwelling individuals. CONCLUSIONS: Falls are an important consequence of bilateral vestibular hypofunction, and patients should be counseled about the increased risk of falling. Assistive devices should be considered, especially for persons aged >65 years with BVL.

Accidental Falls↗
PubMed1999

Oscillopsia and pseudonystagmus in kidney transplant patients.

PURPOSE: Modern immunosuppressants have improved the success of kidney transplantation for renal failure patients. They also may induce neurotoxic effects including tremor. We report two cases of pseudonystagmus and oscillopsia in transplant patients caused by immunosuppressant-induced head tremor and gentamicin-induced vestibulotoxicity. METHODS: Case reports. Head tremor, static visual acuity, and dynamic visual acuity were measured. Vestibular function was evaluated with ice water calorics. RESULTS: Both patients had significant head tremor and pseudonystagmus. Head stabilization improved static visual acuity. Dynamic visual acuity revealed a 4-line and 10-line loss of visual acuity, respectively. CONCLUSIONS: These findings of pseudonystagmus and oscillopsia are likely to become more prevalent as more renal failure patients receive transplants. Improvement may be seen with reduction of immunosuppressant, reduction of stimulant intake, use of medications to reduce head tremor, and vestibular rehabilitation.

Adult↗
PubMed1999

Ocular and oculomotor signs in Joubert syndrome.

A number of oculomotor defects have been described in Joubert syndrome. This study systematically examined the oculomotor systems of 13 individuals previously diagnosed with Joubert syndrome. Twelve had the characteristic "molar tooth sign" seen on magnetic resonance imaging scan. In all individuals, smooth pursuit gain and vestibulo-ocular reflex cancellation were decreased in the horizontal and vertical directions and volitional saccades, when generated, were hypometric. We believe that these defects arise from a disorder in the posterior cerebellar vermis. All individuals also had partial to complete oculomotor apraxia in which initiation of saccades was prolonged or impaired. The oculomotor apraxia in Joubert syndrome differs from congenital idiopathic oculomotor apraxia in that both volitional saccades and quick phases of nystagmus were impaired both in the horizontal and vertical directions, and the defects did not resolve with time. We believe that the oculomotor apraxia arises from a disorder involving the projections from the superior colliculus to the parapontine reticular formation and rostral interstitial nucleus of the medial longitudinal fasciculus. A subset of individuals also had severe visual loss, pendular nystagmus, pigmentary changes in the fundus, and decreased vestibulo-ocular reflexes. We believe that this is a form of Leber's amaurosis occasionally associated with Joubert syndrome. In summary, key oculomotor features of Joubert syndrome are decreased smooth pursuit and vestibulo-ocular reflex cancellation, partial to complete oculomotor apraxia both in the horizontal and vertical directions, and hypometric saccades if oculomotor apraxia is not complete.

Adolescent↗
PubMed1999

Nystagmus: diagnostic and therapeutic strategies.

Nystagmus can have either a jerk (slow and quick phase) or a pendular waveform. Saccadic oscillations can either be back-to-back saccades or have an interval between two saccades. Both nystagmus and oscillations can decrease visual acuity and cause oscillopsia. Each type of nystagmus is attributable to instability or an inadequacy of specific ocular motor systems, including vestibular, optokinetic, smooth pursuit, fixation and the neural integrator. Saccadic oscillations are attributable to instability of the saccadic system. Nystagmus that develops during infancy will not decrease visual acuity if the foveation time within each slow phase is adequate (>60 msec). Infantile nystagmus also does not cause oscillopsia, possibly because the internal spatial visual map is reupdated before each phase of this type of nystagmus (efference copy). There is no foveation period or adequate efference copy reupdate in acquired nystagmus. Consequently, acquired nystagmus usually results in decreased visual acuity and oscillopsia. For most forms of treatment, the goal is directed toward stopping the oscillations or their visual consequences rather than towards the underlying mechanism. Several treatment modalities have been suggested. The most success has been found with gabapentin in the treatment of acquired pendular nystagmus and baclofen in the treatment for acquired periodic alternating nystagmus. There is a need for multicenter trials to evaluate systematically potential treatments of the other types nystagmus and oscillations.

Carbonic Anhydrase Inhibitors↗
PubMed1999

[Diagnosis and therapeutic options in benign paroxysmal positional vertigo].

Benign paroxysmal positional vertigo (BPPV) is one of the most common and treatable causes of vertigo. We examined BPPV types and the effectiveness of physical therapy in each type. BPPV is caused by a utricular statoconium that blocks the semicircular canal. Statoconia can block any of the semicircular canals, but they generally affects the posterior canal. Diagnosis is based on a typical history and characteristic eye movements elicited by the Dix-Hallpike test. Treatment involves a physical maneuver designed to mobilize the free calcium particles from the semicircular canal to the utricle. Canalith repositioning is the mainstay of treatment. The maneuver is illustrated in detail and other forms of treatment and their indications are discussed.

Diagnosis, Differential↗
PubMed1999

The incidence and waveform characteristics of periodic alternating nystagmus in congenital nystagmus.

PURPOSE: To investigate the incidence and waveform characteristics of periodic alternating nystagmus, (PAN) in congenital nystagmus (CN). METHODS: In a prospective study, 18 patients with CN without associated sensory defects agreed to undergo eye movement documentation using binocular infrared oculography. Two of the 18 had a diagnosis of suspected PAN before entering the study. The patients sat in a dimly lit room and viewed an LED (4 min in diameter) located in the primary position, at a distance of 100 cm. During an 8-minute recording, patients were read a story of neutral interest to hold attention at a constant level. PAN was defined as a left-beating nystagmus, a transition phase, a right-beating nystagmus, and a final transition phase; the sequence was then repeated. RESULTS: Seven of the 18 patients had PAN (median cycle: 223 seconds, range 180-307 seconds). The periodicity of the cycles for each adult patient was regular, although the phases within a cycle were often asymmetric. Six of the seven patients had an anomalous head posture (AHP), and in five the AHP was in only one direction. Except for one patient, the PAN waveforms had an increasing slow-phase velocity in at least one phase of the cycle; in the other phase they were linear. CONCLUSIONS: The occurrence of PAN in CN is not as rare as previously thought and can be missed because of the long cycles and the use of only one AHP. The AHP was dependent on, and could be predicted from, the waveforms containing the longest foveation times. Although the waveforms and foveation times may differ among the phases of the PAN cycle, the periodicity of the cycle was usually regular and therefore predictable. Identification of PAN is essential in cases in which surgical treatment is considered for correction of AHPs.

Activity Cycles↗
PubMed1998

Computerized dynamic visual acuity test in the assessment of vestibular deficits.

OBJECTIVE: The study was designed to measure dynamic visual acuity (DVA) during head movement as an assessment of the functional impact of vestibular deficits. STUDY DESIGN: The study design was a prospective, clinical study. SETTING: The study was performed in a tertiary, ambulatory referral center. PATIENTS: Forty-two normal subjects, 29 patients with unilateral vestibular loss, and 26 patients with bilateral vestibular hypofunction who were 19-87 years of age were examined. INTERVENTION: Diagnostic intervention was performed. MAIN OUTCOME MEASURE: Main outcome measures included the reliability, sensitivity, and specificity of a computerized test that measures visual acuity during head movement in normal subjects and in patients with vestibular deficits. RESULTS: The computerized DVA test was reliable in both normal subjects (intraclass correlation coefficient [ICC] r=0.87) and in patients with vestibular deficits (ICC r=0.83). The sensitivity of the DVA test was 94.5% and the specificity was 95.2%. The positive predictive value (individuals who test positive on the DVA test who will have a vestibular deficit) was 96.3%. The negative predictive value (individuals who test negative on the DVA test who will not have a vestibular deficit) was 93%. CONCLUSIONS: The computerized DVA test is reliable and is able to distinguish among normal subjects and patients with vestibular deficits.

Adult↗
PubMed1997

A double-blind controlled study of gabapentin and baclofen as treatment for acquired nystagmus.

We conducted a double-blind crossover trial comparing gabapentin (up to 900 mg/day) to baclofen (up to 30 mg/day) as therapy for acquired nystagmus in 21 patients. We measured visual acuity and the nystagmus before, and at the end of, 2 weeks on each medication. For a group of 15 patients with acquired pendular nystagmus (APN), visual acuity improved significantly with gabapentin, but not with baclofen. Gabapentin significantly reduced APN median eye speed in all three planes, but baclofen did so only in the vertical plane. In 10 patients with APN, the reduction of nystagmus with gabapentin was substantial and 8 of these elected to continue taking the drug. In 6 patients with downbeat or torsional downbeat nystagmus, changes in median slow-phase eye speed were less consistent with both drugs, either increasing or decreasing, and being dependent on viewing conditions. Only 1 patient showed consistent reduction of median eye speed, and this was achieved by either drug. Our findings suggest that gabapentin may be an effective treatment for many patients with APN and that occasional patients with downbeat nystagmus will respond to gabapentin or baclofen.

Acetates↗